Point-of-care (POC) diagnostic devices can be used to address a variety of needs, from water quality to detection of infectious diseases. A long-standing challenge in the area of point-of-care (POC) diagnostics has been the development of operationally-simple and inexpensive platforms for conducting reproducible and rapid quantitative assays. While qualitative assays are available in the form of dipsticks and lateral-flow tests, quantitative assays pose practical challenges that have been difficult to overcome in an inexpensive and convenient way.
In resource-limited environments, POC assays need to be low cost; provide rapid, sensitive results; contain thermally stable reagents; and minimize required equipment and training. Lateral flow assays fulfill these requirements but are unable to quantify analytes within a sample.
Quantitative POC assays typically require the use of an electronic reader capable of analyzing the output of an assay at a fixed assay time. These electronic readers can range from digital cameras (e.g., cell phone cameras) for performing colorimetric assays to digital multimeters for performing electrochemical assays. These readers require a power source, such as batteries, that increases the cost of performing quantitative POC assays. In addition to increased costs, these readers add additional levels of complexity to assays (e.g., proper imaging techniques, analysis of imaging, and preparation of samples for imaging), reducing their applicability in resource-limited environments. The ideal quantitative POC assay, particularly for use in resource-limited environments such as the developing world, not only should be inexpensive, straightforward to operate, and provide rapid and reproducible quantitative results, but it also should do so without requiring use of an external “reader”, such as cell phone cameras, glucose meters, conductivity meters, or any number of specialized electronic devices that could be paired with an assay.